A large amount of research work has been directed toward the development of materials suitable for use in fabricating jet engine parts and other aircraft and aerospace components. A suitable material must be light weight and resistant to oxidation while having high creep, fatigue and tensile strength. Examples of such components include compressor blades, engine casings, heat panels and exhaust gas ducts.
A leading candidate material for the above-mentioned applications is titanium, particularly titanium alloys. However, the use of titanium alloy components is limited by the alloy's high reactivity with oxygen and the formation of an unstable oxide layer, resulting in a degradation of mechanical properties.
As disclosed by C. Hood in Platinum Metals Review 20, 48-52 (1976), various methods have been employed to coat platinum group metals on metal substrates. The following coating methods are disclosed by the author: vacuum deposition, thermal decomposition and chemical vapour plating, electroless plating, aqueous electroplating, fused salt electroplating, metallic bonding and metallizing. These various methods do not provide satisfactory protective coatings for titanium and titanium alloys. There is inadequate cohesion between the coatings and substrate for high temperature, long time exposure so that the coatings tend to separate or spall under these conditions.
In "Ion Implantation", 729-738, Vol. 8 (1973) of a series of books published by North-Holland Publishing Company Ltd. - London, G. Dearnaley et al discuss corrosion studies in ion implanted metals. According to the Authors, the metal ion species, arranged in order of their effectiveness in inhibiting the thermal oxidation of titanium at 600.degree. C are as follows: calcium, europium, cerium, yttrium, zinc, aluminum, indium, nickel and bismuth. While implantation of the metal ions disclosed by the authors do apparently provide a degree of protection against oxidation of titanium, mere ion implantation with the particular metal ions disclosed is ineffective in plating titanium or titanium alloy components with an oxidation-resistant protective coating so as to provide improved mechanical properties.
It is an object of this invention, therefore, to provide a titanium or titanium alloy component having a stable impregnated coating or layer of an oxidation resistant noble metal or an alloy of noble metals without causing degradation of mechanical properties.
Another object of the invention is to provide a titanium or titanium alloy component which, as a result of having an ion plated noble metal or noble metal alloy coating, possesses mechanical properties superior to those of uncoated components.
A further object of the invention is to provide a method for treating components fabricated from titanium and titanium alloys so as to obtain components which are resistant to oxidation and possess improved mechanical properties.